Irenaeus of Lyons, Against Heresies 3.4

Since these demonstrations exist, it is no longer necessary to seek the truth from others, for it is easy to take it from the Church. The Apostles, as though pouring into a rich repository, have fully deposited all things of truth within it, so that anyone who wishes may draw from it the drink of life. For this is the entrance to life; all the rest, however, are thieves and robbers (John 10:1, 8-9). Therefore it is necessary to avoid them, but with the greatest diligence to love and to seize the tradition of truth that belongs to the Church. For what if there were a dispute about some small question? Would it not be necessary to have recourse to the most ancient churches, in which the Apostles conversed, and from them to take concerning the present question what is certain and clear? And what if even the Apostles had not left us the Scriptures? Would it not then have been necessary to follow the order of tradition, which they handed down to those to whom they entrusted the churches? To this ordinance many barbarian nations who believe in Christ assent, having salvation written in their hearts by the Spirit without paper or ink (2 Corinthians 3:3), and diligently preserving the old tradition. They believe in one God, the Maker of heaven and earth and all things that are in them (Genesis 1:1; Acts 4:24), through Christ Jesus, the Son of God. He, because of His surpassing love for His creature, endured the birth from the Virgin, Himself uniting man to God (Luke 1:31-35; John 1:14). He suffered under Pontius Pilate, rose again, was received up in glory, and will come in glory as the Savior of those who are saved and the Judge of those who are judged (Acts 1:11; 1 Timothy 6:14-15; 2 Timothy 4:1), sending into eternal fire the transgressors of truth and the despisers of His Father and of His advent (Matthew 25:41; 2 Thessalonians 1:8-9).

Those who have believed without letters are, as far as our speech is concerned, barbarians; but as far as judgment, custom, and conduct are concerned, because of faith they are most wise and they please God, living in all justice, chastity, and wisdom. If anyone should announce to them the things invented by heretics, speaking in their own language, they immediately stop their ears and flee far away, not even enduring to hear the blasphemous talk. Thus, through that ancient tradition of the elders, they do not even admit into their mind's conception whatever portentous speech is theirs, for there was no assembly among them, nor any instituted doctrine. For before Valentinus, those who are from Valentinus did not exist; nor before Marcion did those who are from Marcion exist; nor were the remaining malignant teachings, which we enumerated above, present to become the initiators and inventors of their perversity. Valentinus came to Rome under Hyginus, and under Pius he prolonged his time until Anicetus. Cerdo, who preceded Marcion, also came under Hyginus, who was the eighth bishop, often coming into the church and making confession; thus he completed his course, sometimes teaching secretly, sometimes making confession, sometimes being reproved by some for the wicked things he taught, and he kept away from the assembly of religious men. Marcion, succeeding him, grew strong under Anicetus, who held the tenth place of the episcopate. The rest, who are called Gnostics, receiving their beginnings from Menander, the disciple of Simon, as we have shown — each one of them, whose teaching he shared, appeared as his father and his bishop. All these, however, rose up much later, in the midst of the Church's times, into their own apostasy.